An agricultural baler is a trailed machine, typically towed behind an agricultural vehicle such as a tractor, used in agriculture for the purpose of forming bales of agricultural crop materials, such as straw, hay, silage or other biomass, produced during a harvesting or mowing operation. A baler typically comprises an infeed through which biomass is introduced into a bale-forming chamber. In the bale-forming chamber the biomass is generally compressed or otherwise treated to form bales. The completed bales are tied with twine or a similar lineal object or are packaged in another way to make them self-supporting. The bales are subsequently ejected by means of a discharge mechanism.
Referring to the drawings, FIG. 1 shows agricultural baler 600 comprising a frame 512 which is equipped with a forwardly extending tongue 514 at its front end with hitch means (not shown) for coupling the baler 600 to a towing tractor. A pick-up assembly 513 lifts windrowed crop material off the field as the baler 600 is travelled thereover and delivers such material into the front end of a rearward and upwardly curved, charge-forming feeder duct 515. The duct 515 communicates at its upper end with an overhead, fore-and-aft extending bale-forming chamber 516 into which crop charges are loaded by a cyclically operating stuffer mechanism 517. A continuously operating packer mechanism 519 at the lower front end of the feeder duct 515 continuously feeds and packs material into the duct 515 as to cause charges of the crop material to take on and assume the internal configuration of the duct 515 prior to periodic engagement by the stuffer 517 and insertion up into the bale-forming chamber 516. The feeder duct 515 may be equipped with means (not illustrated) for establishing whether a complete charge has been formed therein and operating the stuffer mechanism 517 in response thereto. Each action of the stuffer mechanism 517 introduces a “charge” or “flake” of crop material from the duct 515 into the chamber 516. A plunger 562 reciprocates in a fore-and-aft direction within the bale-forming chamber 516. Biomass fed via the feeder duct 515 is thereby compacted, e.g. compressed or otherwise treated, so as to form bales in the above-described operation of the agricultural baler 600. Rectangular bales are formed. The completed bales are tied with twine or a similar lineal object to make them self-supporting, for example for shipping and storage. Once tied, the bales are discharged from the rear end of the bale-forming chamber 516 onto a discharge in the form of a chute, generally designated 520.
The operation of such high density baler results in high loads on the elements of the baler such as the plunger, its drive elements or other elements, which might result in break-down or rapid ageing if the baler is not operated properly. While measuring by sensors and controlled operation based thereon is used in the art, e.g. on the baler chamber, it is known in the field that measuring of loads by load sensors and strain gauges, as for example presented in EP0655190, is expensive and/or requires a complex set-up with careful calibration because of the high loads involved. Furthermore, it has been noticed that, despite the load measurements in EP0655190, gear box shear bolts still break, indicating that unexpected large loads apply to the gear box.